1. Field of the Invention
This invention relates to a gear assembly constituted by a single gear to be mated with a third gear in such a manner that backlash therebetween is eliminated, to reduce noise caused by such a mating. The present invention can be widely applied in various mechanical fields.
2. Description of the Related Art
A conventional non-backlash gear assembly is known, in which the assembly comprises two gears having an identical gear tooth number and profile and a spring anchored at each end to the respective gears, to provide a circumferential biasing force that will tend to rotate the two gears in opposite directions, so that this gear assembly can be mated with a third gear in a nonbacklash manner.
Several types of springs are used for providing a circumferential biasing force between the two gears to realize a non-backlash gear assembly. For example, a compression coil spring is used in the device shown in FIG. 2 of Japanese Examined Utility Model Publication (Kokoku) No. 48-34438 and in FIG. 1 of Japanese Unexamined Utility Model Publication (Kokai) No. 55-158349. A torsional coil spring is used in Japanese Unexamined Utility Model Publication (Kokai) No. 56-160351, and a C-shaped round steel spring is used in FIG. 1 of Japanese Examined Utility Model Publication (Kokoku) No. 48-34438 and in FIG. 3 of Japanese Unexamined Utility Model Publication (Kokai) No. 55-158349. Further, a hairpin-shaped spring is used in Japanese Examined Utility Model Publication (Kokoku) Nos. 48-34438 and 48-2947
A snap spring in the form of C-shaped clip is also known. The present invention is directed to a gear assembly having this type of C-shaped clip snap spring
In a known non-backlash gear assembly including a spring in the form of a C-shaped clip, two circular holes are provided in the spring adjacent to either end thereof and each of the two gears has one pin. Thus each end of the spring can be connected to each gear by the pin and circular hole. This known type of gear assembly has a disadvantage in that the assembly operation is very difficult. Namely, it is very cumbersome to fit the holes to the pins. In the first step the spring is rested on the first gear, and the circular hole of one end of the spring is fitted to the pin on the first gear. This is very easy since both the first gear and the spring can be seen by the operator. In the second step, however, the second gear must be moved onto the first gear, to fit the pin on the second gear into the other hole of the spring. This is very cumbersome since the first gear, the spring and the other pin of the second gear cannot be seen because they are blocked by the second gear, and the operator must fit the other hole to the other pin by touch.
To solve the above difficulty in operation, an improved gear assembly has been proposed in Japanese Unexamined Utility Model Publication (Kokai) No. 61-1770 in which the pins are provided on one of the gears, for example, on the first gear, so that the C-shaped clip spring can be easily positioned and held on the first gear by inserting the pins into the respective holes of the spring. One of the holes is an elongated hole having a diameter larger than the pins, so that the spring can deform when an external force is applied thereto. On the other gear, for example, on the second gear, a C-shaped groove is provided corresponding to the C-shaped spring, to receive the spring in the groove. The spring can be automatically fitted in the groove of the second gear when the second gear is located on the first gear, so that one of terminal ends of the groove bears against the corresponding terminal end of the spring which is displaceable in the groove, resulting in the production of an elastic biasing force due to the presence of the spring between the gears.
However, in this gear assembly, which ensures an easy assembly, a problem arises in that forming the C-shaped groove on the second (or first) gear is relatively difficult. In general, such a curved groove can be formed by a milling cutter, however, since the C-shaped groove has a relatively small width, machining becomes complex and difficult.
Furthermore, in the gear assembly mentioned above, the elastic connection between the two gears is dependent on the spring force of the C-shaped clip spring alone. Therefore, in order to obtain a sufficient spring force, it is necessary to increase the thickness of the C-shaped clip spring, since the plane size of the C-shaped clip spring is limited by the size of the gears. However, if the thickness of the C-shaped spring is increased, it becomes very difficult to form the pin holes on the ends of the C-shaped spring by punching. Namely, the pin holes must be machined by drilling or other mechanical piercing. It is apparent that drilling takes more time than punching, since drilling must be effected for each individual spring, whereas punching can form pin holes in several C-shaped springs substantially at one time. In addition, drilling tends to produce burrs at the edges of the pin holes or tends to produce eccentric pin holes lacking a high precision. This results in a decrease in the surface contact area between the pin holes and the associated pins inserted therein, resulting in an increase in surface pressure therebetween. The increased surface pressure increases frictional wear of the contacting portions between the pins and pin holes.